Polymers derived from unsaturated nitrile monomers, such as acrylonitrile, methacrylonitrile, vinylidene cyanide, etc., are well known in the art. Of this class of monomers, acrylonitrile is presently the most important and is used in making a variety of commercial products, e.g., butadiene-acrylonitrile copolymer rubbers and acrylic textile fibers.
Acrylonitrile has been manufactured by a two-stage process wherein ethylene oxide and hydrogen cyanide are reacted to form ethylene cyanohydrin which is subsequently subjected to dehydration. It has also been manufactured by the direct reaction of acetylene and hydrogen cyanide. However, this latter method of manufacture has not proven promising due to the formation of by-products and the difficulties encountered in separating the acrylonitrile from the by-products, for example, the acrylonitrile tends to polymerize during the multistage stripping and distillation procedures.
There is a large interest in manufacturing acrylonitrile from ammonia and hydrocarbons. One such process involves the catalytic amination of propylene at high temperatures and pressures to form propionitrile, which is then dehydrogenated. Another process involves the reaction of propylene, ammonia and oxygen at high temperatures to form acrylonitrile directly. Although potentially less expensive, the direct methods have the disadvantages of troublesome by-products and requiring expensive equipment.
Another route to unsaturated nitriles is disclosed in U.S. Pat. No. 2,691,037. This patent teaches a process for preparing unsaturated nitriles from unsaturated aldehydes in the vapor phase, in which the aldehyde is reacted with ammonia and molecular oxygen at elevated temperatures in the presence of a metal or metal oxide catalyst such as, e.g., copper.
A liquid phase, low temperature route to aromatic nitriles from aromatic aldehydes is reported in RECUEIL, v. 82, pp. 757-762 (1963). In this process, a copper-ammonia complex catalyst and a strong base are employed in a methanol solution. However, this process proved unsuccessful when applied to an unsaturated aldehyde, namely acrolein, only a "trace" of acrylonitrile being produced. More recently, benzaldehyde ammoxidation to benzonitrile was reported in Bulletin of the Chemical Society of Japan, v. 40, pp. 912-919 (1967), using a liquid phase process in a methanol solvent, and employing various copper salts as a catalyst.
While such liquid phase, copper catalyzed processes have proven successful for preparation of saturated or aromatic nitriles, the high reactivity of the olefinic double bond of unsaturated nitriles such as acrylonitrile, methacrylonitrile, and the like has prohibited the use of such processes to produce these compounds. For ammoxidation of the highly reactive unsaturated aldehydes, it is necessary to keep the level of free ammonia quite low in order that the unsaturated aldehyde does not undergo an ammonia catalyzed polymerization such as is reported by C. W. Smith in his book "Acrolein", John Wiley & Sons, New York (1962) at pp. 13-15; in accordance with the present invention this may be done by employing a copper-ammonia complex catalyst which serves both as the catalyst and as the source of ammonia for the ammoxidation reaction. The copper-ammonia complex may advantageously be preformed prior to addition of the unsaturated aldehyde to be ammoxidized; alternatively, the complex may be formed during the ammoxidation by slow, controlled addition of ammonia to the reaction mixture.
Accordingly, it is an object of this invention to provide a simple, economic liquid phase process for the production of olefinically unsaturated nitriles.
It is also an object of this invention to provide a process for the preparation of unsaturated nitriles from corresponding unsaturated aldehydes in high yields and substantially free of undesirable by-products.
Other objects and advantages of the invention will become apparent from the following detailed description.